The exclamation rises from the stands at Turkish football games, when a player misses a pass or a referee makes a questionable call. Just as voters do in a democracy, fans want to express their views about what's happening on the field.

Turks will get the chance to make their voices heard on Sunday, April 16, when millions will cast their votes in a referendum on whether the Turkish government should switch from a parliamentary to a presidential system. Supporters of a presidential system say it will bring stability to Turkey's chaotic politics, and provide strong leadership against threats foreign and domestic. Those against a presidential system, who want to maintain the current one, say that it will lead to "one-man rule" and undermine Turkish democracy.

The ballots are simple: "Yes" ("Evet") or "No" ("Hayir"). Banners with the words cover public spaces in Istanbul. Evet banners feature images of Turkish President Recep Tayyip Erdogan and Prime Minister Binali Yildirim, sometimes alongside the slogan: "For our future." The "Hayir" banners show the face of a smiling little girl, and a similar slogan: "For my future."

Hayir voters see the current parliamentary system as a guarantor of Turkish nationalism and secularism, and want to see Turkey in the orbit of Europe. Evet voters want to maintain reforms under Erdogan that gave more space to traditional, conservative parts of the the country.

These two poles of Turkish society don't always share the same priorities and concerns, and they have struggled to work together since the founding of the republic.

As Turkey's economy has grown, it has lifted the religiously conservative lower classes into a position where they have a greater voice in politics, more time and money to spend on having a say. They have clashed with a secular elite that turns more to Europe than the Middle East. Economic development has transformed Turkish society, and disagreement over the nature of Turkish identity seems as inevitable as it is intractable.

A poster urging passage of the referendum outside the Kasimpasa stadium in Istanbul. (Photo by Wilson Dizard)

Two football teams named after two neighbourhoods in Istanbul embody the two sides. One team, Besiktas, represents a neighbourhood filled with bars and restaurants, full and loud even on weeknights. Another club, Kasimpasa, represents a more conservative, quiet neighbourhood just a few kilometres away. It's also the area where Erdogan grew up.

"As people of Kasimpasa, our vote is obvious. Recep Tayyip Erdogan was born here, my uncle was classmates with him, they went to school together. My vote is ‘yes'. As I researched it, I saw that countries with presidential system have developed greatly," said Emre Sevimliot, 21, at a stadium named after the Turkish president.

"Also, if Europe is criticising this system, that means there must be something good for our country. Because they don't want us to get better."

Sevimliot was sipping tea during half time with his friend Mücahit Ateş, 20.

"I'm going to say similar things," Ates said. "My grandparents knew him [President Erdogan] since the days he was selling simit (a bagel-like street snack) on these streets and supported him since then. So did we. If 'yes' wins, the dual-headed system will end. The book incidents will not happen again. We will vote 'yes' so that our country can see more development."

Emre Sevimliot, 21, and Mucahit Ates, 20. (Photo by Wilson Dizard)

The "book incident" was a 2001 dispute between the Turkish president and prime minister which involved one hurling a copy of the constitution at the other. The instability caused the Turkish economy to go into free fall. A switch to a single presidential system would make future disputes between prime minister and president impossible, supporters say, because it would eliminate the office of prime minister.

The Hayir side broadly represents the political opposition, the former Turkish political establishment, and they worry that the changes will permanently shut them out of power. The Evet side wants to solidify reforms under Erdogan that allowed elements of Islam into public life, such as the lifting of a ban on wearing hijab in government buildings and institutions. The opposition sees these changes as challenges to the secular state.

While the two neighbourhoods represent the secular and pious sides of Turkish society, the opinions of fans of their respective teams are not uniform. Some Besiktas fans want Evet, and some backing Kasimpasa want Hayir.

"I will vote 'no'. Until now, I kept saying 'yes, yes, yes' to everything this government said. But not this time. I will vote ‘no' because maybe that's what needs to happen for some things to change. I think this referendum is not about policies, it's more about individuals, political figures," said a 26 year-old Kasimpasa fan.

Some of the reasons for voting "no" come from concerns about immigration by Syrian refugees into Turkey. Right now, about three million Syrians live in Turkey, many of them in Istanbul. The newcomers stoke cultural resentments among nationalist Turks.

"I'm undecided but leaning towards 'no'. Because I have a nationalistic mindset. We started drifting and living away from our own values. We admitted too many guests (Syrians) – I can get on the bus from where my shop is, and come [here to the stadium] as the only Turk on the bus. This bothers me. I believe our old system was correct," said 36-year-old Ali.

When we spoke with Kasimpasa fans, the team had just finished a game against Konyaspor, ending in a 1-1 tie. The fans, who were mostly men, filed out of the stadium without much emotion, possibly because the game resulted in a draw, headed home on the Monday night. The most intoxicating beverage available at the stadium was strong Turkish tea.

When we spoke to Besiktas fans on the Saturday before, April 9, the team had just won a stunning victory against Trabzonspor, in an away game. Bars and restaurants erupted in cheers across Besiktas when the team triumphed 4-3. The energized, somewhat inebriated crowd gathered in the centre of the neighbourhood to chant and wave their team's white, black and red flags.

Most of the Besiktas fans we spoke to expressed intentions to vote Hayir, but some said they were planning on voting Evet. In one case, the split revealed a generational difference.

Two Besiktas fans, a father and son, were celebrating in the street after the game. The father was swinging a Besiktas flag outside a shop.

Emre and Bekir Erguc, son and father, after a Besiktas game. (Photo by Wilson Dizard)

Another person put the same sentiment a different way.

"I don't want one-man rule. If Evet wins, it's going to be like the Ottoman sultan times. It's old fashioned and I don't like it," said Akin Gul, 42.

The vote has also divided married couples.

"I am against anything that the enemies of Turkey support," said Bahar Battal, 23.

Her husband, Ibrahim, disagreed, saying that Erdogan has amassed too much power already

"He's basically doing anything he wants," Ibrahim said

Besiktas fans feel that the nature of their neighbourhood and their fan base is in opposition to abuses of authority. This process began almost 40 years ago, according to Yakup Aras, 42, when the military staged a coup and threw thousands of Turkish citizens into jail.

"After 1980 coup, most of democrats and revolutionaries preferred to be in Besiktas stands. That's why Besiktas stands became democrats. That's why ‘no' rate is very high," Aras said. "Since they are democrats, they constantly clash with the system."

More of the Kasimpasa fans expressed undecided opinions than those in Besiktas. For Besiktas fans, they feel a severe sense of urgency that, if Evet should win, their way of life would be under threat along with the republic.

"Of course ‘no.' I can't tolerate that the Turkish Republic is handed over to one man. I can't tolerate it even if it's my father. That's the most important reason," said Verda Taşlı, 52. "If ‘yes' wins, there's nothing we can do. It means the country is done."

Verda Taşlı, 52, right, and a friend after a Besiktas game. (Photo by Wilson Dizard)

To both sides, the outcome of the referendum feels like a "winner-take-all" contest. It comes in the wake of other significant elections across the world, from the Brexit vote in Britain to the 2016 election in the United States. In the days and hours before the polls close, campaigners on both sides are holding rallies and hitting the streets with fliers and friendly faces trying to convince voters that their side is right. Polls show both sides are nearly neck and neck.

Turkish democracy has faced multiple challenges over the last few years, including an attempted coup last summer, terrorist attacks and a polarised public. But these challenges are not new in the history of Turkish democracy. What the referendum reveals is how Turks have been able to defy cynicism and respond with sincere passion to the task of participating in public life, shaping the future of their country.

In Besiktas, at the corner of the coast road and Barbaros Boulevard, Evet and Hayir campaigners have set up tents next to each other, and they alternate playing songs in support of their cause. Both sides fly the Turkish flag with pride. They remain civil and respectful of each other, despite vehement disagreements on political issues.

Looking at both Besiktas and Kasimpasa at a glance, one would expect one to be entirely Hayir and the other entirely Evet. But the diversity of opinions in both places reveals how Turks maintain a culture of independent thought, and aren't simply following their neighbours or their families. It's evidence that no matter which side wins on Sunday, Turks are extremely passionate about their country and want to have a voice in its future.